1. Field of the Invention
This invention relates to an improved process for separating hydrocarbons into fractions having different boiling points. More particularly, this invention relates to an improvement in a distillation process.
2. Description of Information Disclosures
Processes are known for separating mixtures of hydrocarbons into fractions having different boiling point ranges by subjecting the hydrocarbon mixture to a distillation zone to produce a vapor phase fraction, one or a plurality of liquid sidestreams, and a heavy bottoms fraction. It is also known to separate under vacuum the heavy bottoms fraction into additional fractions.
U.S. Pat. No. 2,073,622 discloses a process for cracking hydrocarbonaceous oils. The bottoms from a cracking chamber are withdrawn through a pipe and a pump. A portion of the bottoms is passed through a furnace to the top of a separator. When a valve is open, an other portion of the bottoms passes into the bottom of the separator.
U.S. Pat. No. 2,900,327 discloses removing bottoms from a fractionator in two separate streams. One stream is passed through a furnace. The other stream by-passes the furnace and is introduced into a stream which leaves the furnace. The combined stream enters a separator.
U.S. Pat. No. 2,160,256 discloses a caustic stream in line 112. One portion of the stream passes through a heater. An other portion of the stream by-passes the heater.
U.S. Pat. No. 2,341,389 discloses a process for fractionating light hydrocarbon oils comprising two fractionators with an intermediate furnace.
U.S. Pat. No. 4,662,995 discloses a method and apparatus for separating hydrocarbon mixtures by distillation, steam stripping a sidestream, returning a vapor separated in the sidestream stripper to the distillation zone at a location at least two trays and/or at least one theoretical stage above the liquid draw-off from the distillation zone to the sidestream stripping zone.
Although some of these processes increase the amount of lower boiling components that can be separated from the heavier fractions, there is still a need to improve the separation of lower components from the higher components.
It has now been found that the amount of lower boiling components that can be separated from the higher boiling components can be increased, in a hydrocarbon separation process, in which the heavy bottoms fraction of an atmospheric distillation zone is heated in a heating zone, such as a furnace, and subsequently passed to a vacuum separation zone, if a portion of the heavy bottoms fraction by-passes the heating zone and is introduced directly into the vacuum separation zone. This permits the total feed rate of the heavy bottoms portion to the vacuum separating zone to be increased. It also permits a decrease of the rate at which a conventional quench recycle stream can be introduced into the vacuum separation zone.